OCR Text |
Show e) Powder avalanche at Mauvoisin ( see Fig. A) In February 1954 a snow cover of 1.7 m depth and about 100 kg/ m3 average density lay at Mauvoisin. At about 2500 m above sea level an avalanche released, formed a powder avalanche on a rock slope with an average inclination ^ 0 = 47° and after striking the bottom of the relatively narrow gorge ( valley floor 1740 m above sea level) was propelled upward on the opposite slope with an average inclination ^ u = 36° to a height of 1960 m above sea level. According to Equation ( III, 11) the maximum velocity was 53 m/ sec. The horizontally measured run out distance according to Equation ( VII) is: s = 170 m, The powder avalanche thus climbed on the opposite slope to a height s . tan + u = 120 m above the valley floor; the uppermost part of the powder avalanche reached the damming height v2/ 2g = 140 m higher. Consequently the calculated total height of the powder snow cloud reached 260 m, i. e., it reached at the highest point the 2000 m contour line, which agrees approximately with observation. Powder avalanches are, in the limiting region of the highest damming as a result of the dissipation of the kinetic energy, relatively harmless. f) Snow pressure measurements on an impact plate ( SFL) Terrain gradient Wet snow Equation ( III) Equation ( VIII) \ k0 = 45 - 500, % = 240 Y0 = 400 kg/ m3, p. ~ 0, h - 0.7 m v = 22 m/ sec p = 12,000 kg/ m2 Measured maximum pressure: p = 11,825 kg/ m2 g) Experience with supporting structures ( avalanche defense structures) Of the countless structures which have been exposed to the pressure of snow, three supporting structures, constructed with various materials according to the prevailing hypothesis of the load, which suffered exceptional damage and which permit an estimate of the loads experienced owing to their statically determinable construction for a factor of safety of 2 or 3, are referred to here. The new snow ( Y 0 ~ 2 0° kg/ m3) » ( P- ~ Yo/ 2000) laY 1.5 m deep. After the damages had been sustained snow slab fractures were determined to have occurred about 50 m above the structures; in the first instance the fracture was 50 cm high, in the second 1 m high and in the third case snow drifts up to 10 m in height lay above the structure concerned. ( 1) Supporting structure constructed for a snow pressure of 1.2 t/ m2 with a structure height d0 = 3 m, measured perpendicular to the 65 to 70% slope Snow slab of 1/ 2 m flow height Eq. ( Ill ): v = 11 m/ sec 55 |